ARCHIVED - Health Canada Scientific Summary on the U. S. Health Claim for Sodium and Hypertension

Bureau of Nutritional Sciences
Food Directorate, Health Products and Food Branch
Health Canada

April 2000

Executive Summary

Since the US. Health Claim on sodium and hypertension was accepted in 1993, considerable research has been completed clarifying those who respond to changing sodium intakes with changes in blood pressure, factors affecting this response, quantifying short term and long term blood pressure changes in response to dietary sodium restriction in normotensive and hypertensive populations, and clarifying the role of other risk factors for hypertension. Risks associated with low sodium intakes as well as excessive intakes have also been identified.

Hypertension is a risk factor for stroke, coronary artery disease, peripheral vascular disease, congestive heart failure and renal failure and as such is considered a major public health problem. Hypertension affects approximately 22% of Canadian adults, the incidence increasing with age such that by age group 55 to 64 years, 46% of that population has hypertension. An additional 26% of adults have diastolic pressure in the high normal range. Risk factors for hypertension include overweight and obesity, alcohol in excess of 2 drinks per day, physical inactivity, adult onset diabetes, poor nutrition, including excessive sodium intakes at least in certain segments of the population, and inadequate intakes of other dietary components particularly potassium and possibly calcium.

The fundamental question addressed by this report is whether lowering sodium intake in a whole population will reduce risk of hypertension. Four meta analyses of randomized controlled trials have been conducted since 1993, and consistently show a small, statistically significant reduction in systolic blood pressure (about 1.2 mm Hg)  in normotensive individuals for a large (100 mmol or about 6 g salt) reduction in sodium intake over the short term. Over the longer term of 3 years, although some reduction in population sodium intake is achievable (25-50 mmol/d), the effect on blood pressure is very small (1 mm Hg systolic) compared to usual care, and not significant as a main effect.

In hypertensive individuals, from the same 4 meta analyses, a consistent and more robust effect of sodium reduction on blood pressure was seen in the short term.

Biological differences in blood pressure response to sodium have been identified recently, such that a sub-group of both the normotensive and hypertensive population show a marked blood pressure rise with relatively high sodium intake. Sodium sensitivity is a reproducible phenomenon, but is also influenced by nutritional status, particularly potassium and calcium intakes, by age and by overweight/obesity. Prevalence estimates of sodium sensitivity are 15-35 % of the normotensive population and 29-50 % of the hypertensive population.

Potential risks of sodium reductions have recently been suggested from three prospective cohort studies and one meta analysis. The inverse association of all-cause mortality with sodium intakes, suggests that sodium restriction may be harmful under some circumstances, but these observations need further study.

Although expert views and interpretations of this data are not consistent, there is substantial evidence that reducing sodium intake in at risk populations has a minimal effect on population mean blood pressure at current levels of intake, (4.1 g sodium or about 10 g salt/d in the 3 year study above). Based on recent estimates of sodium intake, over 25% of Canadian men age 18 to 49 consume excessive sodium (over 10 g salt/d), as do 10% of men over 50. Given that between 15 and 35% of the Canadian population may be salt sensitive, and that  22% of the population has hypertension, a prudent population-based strategy to reduce risk of hypertension is to avoid excessive sodium intakes.

Thus a prudent claim is "moderation in intake of sodium may reduce the risk of high blood pressure, a condition associated with many factors including overweight, excessive alcohol consumption, inadequate intake of dietary potassium, and inactivity".*

Other interventions such as weight reduction are effective in both the short and long term. A well-substantiated claim for the Canadian population is: Attaining and maintaining a healthy body mass index will reduce the risk of hypertension, a condition associated with many factors.

*Important note: This claim was the subject of a regulatory amendment. For the final wording and conditions of use for this claim, please refer to the table following section B.01.603 in the  Food and Drug Regulations.